1. Field of the Invention
The present invention relates to a beamforming apparatus and method for a multi-antenna system, and more particularly, to a beamforming apparatus and method which performs radio frequency (RF) beamforming by using one analog-to-digital (A/D) converter and decides a phase weight vector capable of acquiring a maximum signal-to-noise ratio (SNR), in a multi-antenna system using a plurality of antennas.
2. Description of the Related Art
In general, a wireless communication system using multiple antennas or spaced antennas (hereinafter, referred to as “multi-antennas”) for high-speed wireless communications is being developed. Beamforming is one of several technologies using multi-antennas and is widely known as a method in which a receiver or transmitter uses multi-antennas to increase connection reliability in wireless environments.
Worldwide interoperability for microwave access (WiMax) standard, long-term evolution (LTE), IEEE802.11n WLAN, IEEE802.15.c WPAN and so on may be taken as examples of wireless environments in which such multi-antennas are used. In order to implement a multi-antenna system, an equal number of RF chain units configured with a low noise amplifier (LNA), a mixer, a filter, an intermediate frequency (IF) signal, and an A/D converter are needed. Therefore, the price, power consumption, and size of a multi-antenna system are being considered as problems in implementing the multi-antenna system.
In particular, it is known that an A/D converter has the highest power consumption when processing baseband signals. To minimize this power consumption, analog beamforming or RF beamforming technology employing a minimum number of RF components may be used. In the existing baseband beamforming technology, signals received by antennas should be converted into digital signals through an A/D converter so as to calculate a weight vector which maximizes an SNR.
However, when the analog beamforming technology is used, the phases of signals received by antennas are converted by phase shifters and then summed. Therefore, only one A/D converter having high power consumption may be used. Accordingly, research and development on the analog beamforming technology has been conducted intensively.
In the baseband beamforming technology according to the related art, signals received by multi-antennas may be converted into digital signals through an A/D converter so as to acquire an optimal weight vector through eigenvalue decomposition. When this technology is used, the direction of a signal received by an antenna may be accurately estimated. Therefore, it is possible to improve the performance of the multi-antenna system. However, when the analog beamforming is used, the eigenvalue decomposition cannot be used. Therefore, there is a demand for a new method for acquiring an optimal weight vector.
In a technique which estimates a weight vector using the analog beamforming technology according to the related art, all possible vectors are applied to find an optimal vector.
However, since finding an optimal vector for all vectors may increase the complexity of a system, it is difficult to apply to an actual system.